In recent years, solar power generation systems have been spreading as a means of power generation utilizing clean energy. As described in JP-UM-6-38264, for example, a solar cell module generally has a structure in which a plurality of plate-like solar cell devices are sandwiched between a light-receiving-side glass substrate and a backsheet, with the interspace being filled with an encapsulating resin.
Further, as a backsheet of a solar cell, use of a polyester film is known (JP-A-2001-148497, JP-A-2001-257372, and JP-A-2003-60218). These polyester films are still insufficient in terms of hydrolysis resistance for long-term use, and attempts for improvement have been made. It has been proposed to use a high-molecular-weight polyethylene terephthalate film (JP-A-2002-26354), a polyethylene terephthalate film having a low oligomer content (JP-A-2002-100788, JP-A-2002-134770, and JP-A-2002-134771), and a polyester film containing 2,6-naphthalene dicarboxylic acid (JP-A-2007-007885 and JP-A-2006-306910). Further, a white polyester film having high reflectance has also been proposed, which is advantageous in terms of the efficiency of conversion of sunlight into electricity (JP-A-2002-26354 and JP-A-2006-270025).    Patent Document 1: JP-UM-6-38264    Patent Document 2: JP-A-2001-148497    Patent Document 3: JP-A-2001-257372    Patent Document 4: JP-A-2003-60218    Patent Document 5: JP-A-2002-26354    Patent Document 6: JP-A-2002-100788    Patent Document 7: JP-A-2002-134770    Patent Document 8: JP-A-2002-134771    Patent Document 9: JP-A-2007-007885    Patent Document 10: JP-A-2006-306910    Patent Document 11: JP-A-2002-270025